1. Field of the Invention
This invention relates to a compact and easily manufacturable illuminating device suitable for the illumination of an original in an original reading optical system used in a copying apparatus, a facsimile apparatus or the like.
2. Description of the Prior Art
In a copying apparatus or a facsimile apparatus, formation or reading of the image of an original is effected while the original is scanned in at least one direction and therefore, an illuminating device capable of efficiently illuminating a linear particular area has been required and, to this end, an illuminating device, as shown in FIG. 1 of the accompanying drawings has been used. Referring to FIG. 1 which is a cross-sectional view, a linear light source 16 and a reflecting mirror 17 extend in a direction perpendicular to the plane of the drawing sheet. The linear light source 16 is, for example, a fluorescent tube having an elongated light-emitting portion. The reflecting mirror 17, as shown, has its reflecting surface of elliptical cross-section continuous in a direction perpendicular to the plane of the drawing sheet. The light emitted from the linear light source 16 is reflected by the reflecting surface of the reflecting mirror 17, is converged and illuminates only a linear particular area.
However, in the conventional illuminating device as described above, the reflecting mirror has been formed by plating the inner surface of a metal plate or the like, and this has led to a disadvantage that it is difficult to bend the metal plate into a distortion-free elliptical cross-section as shown and its productivity is poor. Also, in the combination of the reflecting mirror with the linear light source 16, it has been necessary to spatially adjust its position and fix it so that the light-emitting portion of the light source 16 in its cross-section is coincident with one focal point of the elliptical cross-section of the reflecting mirror 17, and this also has led to a disadvantage that the assembling process becomes complicated.